DE 199 56 859 A1 (corresponding to U.S. Pat. No. 6,799,687) discloses a filter device having conically shaped filter elements, in particular in the form of tubular wedge wire screen filter elements. Due to the conical execution, the distance between the individual conical, tubular wedge wire screen filter elements is increased in individual areas, with the result that the outflow space in the filter housing is also enlarged. During backflushing, the conical filter element is distinctly advantageous compared to a cylindrical one, primarily because the relatively large exit cross section of the conical filter elements relative to the cylindrical ones for the same filter surface. Since the exit cross section for conical filter elements relative to the entry cross section formed by the filter surface, i.e., the free element area, however, is small, depending on the amount of flow resistance of the split tube, a bottleneck forms in which a large part of the system pressure drops. Therefore, smaller pressure losses occur that is more favorable in terms of energy in backflushing.
In backflushing, a large part of the volumetric throughput for conical and for cylindrical filter elements is generally achieved on the lower filter end. The volumetric flows then decrease very quickly. In addition, for conical elements the velocity gradient is smaller, so that including the velocity profile, relative to the filter surface, an additional cleaning effect compared to cylindrical elements arises due to the conicity of the elements. Due to the essentially constant velocity that is achieved in the cleaning of the conical filter elements, this cleaning takes place carefully and prolongs the service life of the pertinent filter elements.
In backflushing, preferably all filter elements are regenerated in succession. During backflushing of individual elements, filtration is continued via the remaining elements so that filtration operation is not interrupted at any time.
In the known filter device, the backflushing process does not take place exclusively such that the overpressure prevailing in the filter device during the backflushing phase allows a partial stream of the filtrate to flow through the filter element to be cleaned in the reverse direction to detach and carry away dirt from the element. In the effort to be able to remove even the most stubborn dirt, to support backflushing, a pressure control means generates a negative pressure on the respective filter element to be backflushed. Therefore, not only is the system pressure active in backflushing, but a higher pressure gradient for detaching dirt is available due to the applied negative pressure.
In the known device, the negative pressure means has a hydraulic accumulator in the form of a diaphragm accumulator. The diaphragm forms the separating element of the accumulator for intake or pump motion and is connected to the piston rod of a working cylinder. For this actuation, not only is a considerable control effort necessary, but to ensure operating reliability, a complex construction of the diaphragm accumulator with a piston rod duct and its sealing is necessary. In spite of an expensive construction, relatively long service lives ensuring operating reliability can hardly be achieved. Moreover, considerable installation space for the accumulator and the drive means is necessary.
DE 10 2005 016 151 A1 discloses a filter device with a housing and a filter inlet for the fluid to be filtered, as well as a filter outlet for the filtered fluid. Within the filter housing, several filter elements are provided. The respective filter element having a first through opening is fluid-connected to the filter inlet and through which during the filtration process dirty fluid flows from the inside to the outside. A movable flushing arm with a fluid opening for backflushed dirty fluid can be fluid-connected to the first passage opening of the filter element. As a result a backflushing flow from the outside into the interior of the filter element arises. Because the respective filter element has a second passage opening and one valve unit in the filtration process closing the second passage opening and opening it in the backflushing process, by opening the valve unit in the backflushing process, a second access possibility of the backflushed fluid via the second passage opening enables an additional backflushing flow within the filter element for obtaining a high degree of cleaning in the backflushing process.
DE 100 24 401 A1 discloses a generic backflushing filter device, in particular for lubricating oil filtration. Filter cartridges open on both ends are located in the filter housing around a rotary shaft. Each filter cartridge interior in filter operation can be supplied with the heavy liquid to be filtered. Liquid can flow into the backflush filter with a cleaning means moved by the rotary shaft. For individual or group cleaning of the filter cartridges in backflushing operation, the rotary shaft has at least two flush cocks connected to a drain valve via the rotary shaft. The first flush cock is assigned to one end side of the filter cartridge. The other flush cock is assigned to the other end side of the filter cartridge. Because the first flush cock is arranged offset by an angle in the direction of rotation to the second flush cock, and concomitantly moved first and second sealing members are assigned to the first and second flush cocks for the opposite end side of the filter cartridge. That offset of the flush cocks by an angle in the direction of rotation permits the filter cartridges to be exposed to the flushing pressure in a delayed mode on the two inflow ends. With this backflushing in opposite directions in a delayed mode, high flushing velocities or velocity profiles are achieved over the filter cartridge height. This operation has a beneficial effect especially in the middle regions between the inflow ends due to the higher flushing velocities active there for an improved flushing effect.